The features of the present invention are particularly useful as applied to the construction of incandescent lamps employed in automobiles, such as the dual-filament lamps employed in tail light assemblies.
One well known example of existing lamps of this type generally employed a type S-8 glass bulb cemented in a brass, double contact bayonet base. Although used for a number of years, such bases pose a number of disadvantages. For example, anyone who has replaced such a lamp in their automobile will appreciate the great difficulty experienced in position-referencing the base to insure the proper lamp-to-socket orientation. The base is cylindrical and the only orientation reference means are small indexing pins at the sides of the base. This referencing problem also holds true for automatic insertion of the lamp into the socket during production thereof. Further, the lamp to base construction for dual filament lamps of this type requires three soldering points for electrical connections (the two lead-in wires serving as the common connection are twisted and soldered to the sidewall of the base, while the other two wires are respectively soldered to the twin contact nodes at the bottom of the base). This leads to corrosion or other contact degradation problems caused by soldering fluxes. Finally, the bayonet base lamp requires a somewhat complicated and relatively expensive socket design.
One attempted solution to the several aforementioned problems inherent in brass base lamps is defined in U.S. Pat. No. 4,028,577 (P. E. Gates et al), said patent assigned to the same assignee as the instant invention and being a continuation-in-part of U.S. Pat. No. 3,979,627 (S. J. Leadvaro et al). In U.S. Pat. No. 4,028,577, there is described an electric lamp having a sealed end containing therein (or extending therefrom) a reentrant glass stem sealed about its periphery to the glass bulb. This end is positioned within a plastic base having a cylindrical body portion (for housing the somewhat cylindrical-shaped sealed end) and adjacent wedge portion. While this concept proved advantageous in several ways over the aforementioned brass base lamps, it was necessary to provide additional features, steps, etc. in order to satisfactorily produce and utilize this arrangement. For example, it was necessary to position the extending tip segment (from the sealed end) a sufficient distance from the base's inner, bottom wall in order to provide protection thereof. Maintenance of this distance was assured by cementing the bulb (along the outer walls) to the base. It was also necessary in this design to pass the lamp's projecting lead-in wires through corresponding passages (holes) within the base, thus mandating a relatively complex (and time-consuming) alignment and insertion procedure. Even further, final lead-in wire retention necessitated yet another production step (e.g., heat staking) which added still further to the cost of this lamp.